1. Field of the Disclosure
The present disclosure relates to a post-processing device for performing post-processing on sheets. Further, the present disclosure relates to an image forming apparatus including a post-processing device. Further, the present disclosure relates to a control method for a post-processing device for performing post-processing on sheets.
2. Description of Related Art
An image forming apparatus such as a multifunction peripheral, a printer, a copying machine, and the like may be provided with a post-processing device. The post-processing device performs, for example, punching processing, stapling processing, and sorting processing when receiving printed sheets (paper) delivered from the image forming apparatus. Further, post-processing is performed on a plurality of sheets, and hence a tray for stacking the plurality of sheets may be provided inside the post-processing device. When the number of sheets (number of pages) of one copy exceeds the maximum number of stacked sheets of the tray, the post-processing cannot be performed on the whole sheets of one copy, with the result that desired post-processing cannot be executed in some cases.
To address this problem, there is known a sheet processing device capable of performing sorting processing even when the number of sheets of one copy exceeds the maximum number of stacked sheets. For example, there is known a sheet processing device including a collection tray for collecting sheets, a processing tray for temporarily stacking the sheets in the course to the collection tray, shifting means for shifting, on the processing tray, a collection position of the sheets in a width direction thereof, and capacity recognizing means for recognizing a stack amount of sheets stacked on the processing tray. The sheet processing device sorts the sheets for every predetermined number of sheets, and when the capacity recognizing means recognizes that the stack amount of the sheets on the processing tray exceeds a limit stack amount of the processing tray, the sheet processing device delivers the sheets stacked on the processing tray to the collection tray, and continues operation of the shifting means so that the position of the delivered sheets and the position of succeeding sheets are aligned on the processing tray until the number of the succeeding sheets reaches to a predetermined number. With this configuration, the sorting processing is adapted to the case where the number of sheets exceeds the limit stack amount of the processing tray.
Conventionally, in order to deliver the sheet bundle from the post-processing device, a printing speed of the image forming apparatus may be decreased (for example, a sheet feeding timing and an image formation start timing are delayed as compared to a normal case) so that an inter-sheet gap is increased. For example, in the conventional sheet processing device, in order to deliver the sheet bundle, a waiting time is provided on a boundary between copies. Further, in the conventional sheet processing device, in a case where the number of sheets of one copy exceeds the limit stack amount of the processing tray, when the sheets are stacked on the processing tray up to the limit stack amount, the printing is temporarily stopped for advancing the sheet.
As described above, in the conventional post-processing device, the printing in the image forming apparatus is temporarily stopped to deliver the sheet bundle. In other words, the inter-sheet gap between the sheets is increased as compared to the normal printing to ensure a period of time for delivery of the sheet bundle from the processing tray.
In order to maintain productivity (in order to maintain a normal inter-sheet gap), the post-processing device may be provided with a turn-aside portion for temporarily turning aside the sheet before the sheet is accumulated on the processing tray, to thereby delay the arrival of the sheet at the processing tray. However, when a plurality of copies are continuously printed, the following problem may arise in the post-processing device. That is, when the last page of one copy is turned aside, the last page of the one copy overlaps the first page of the succeeding copy, with the result that the last page of the one copy and the first page of the succeeding copy are transported with no difference in time. Consequently, the sheet bundle delivery (sorting) cannot be performed for each copy.
Therefore, in a case where the sorting is performed, when the sheet bundle is delivered at a point at which a page preceding the last page is stacked, the last page cannot be turned aside. In view of this, in order to ensure the period of time for delivery of the sheet bundle (in order to delay the arrival of the last page at the processing tray), the inter-sheet gap between the last page and the page preceding the last page always needs to be set larger than the normal case. Therefore, there is a problem in that even the turn-aside portion cannot maintain the productivity in some cases when the number of sheets of one copy exceeds the maximum number of stacked sheets of the processing tray.
The above-mentioned publicly known sheet processing device is not provided with the turn-aside portion. Hence, such a sheet processing device is not relevant to the problem of the decrease in productivity in the case of delivering only the sheet on the last page. Thus, the above-mentioned publicly known sheet processing device cannot solve the above-mentioned problem.